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'use strict';
const parser = require('accept-language-parser');
const _ = require('lodash');
const { languageCodeExists } = require('country-language');
const DEFAULT_LANGUAGE = 'en';
module.exports = setup;
/**
* Intersect the list of user accept languages over the list of authorized languages
* and return the first matching language
*
* iterate over the ordered list of user accepted languages and:
* 1/ find exact match (country + region)
* 2/ find partial match (country code)
*
* @param {Array} authorizedLanguages Array of authorized/known languages.
* @param {Array} userAcceptLanguages Array of parsed languages from Accept-Language.
* @returns {String|null} The first matching language if found, null otherwise.
*/
function findLanguageMatch(authorizedLanguages, userAcceptLanguages) {
for (const language of userAcceptLanguages) {
// find exact matching
const foundExactLanguage = _.find(
authorizedLanguages,
lang => lang === `${language.code}-${language.region}`
);
if (foundExactLanguage) return foundExactLanguage;
// compare language country code only
const foundCountryCode = _.find(authorizedLanguages, lang => {
// eslint-disable-line no-loop-func
const parsedLanguage = _.get(parser.parse(lang), '[0]');
return parsedLanguage.code === language.code;
});
if (foundCountryCode) return foundCountryCode;
}
return null;
}
/**
* Setup language middleware
* @param {Object} opts the language options
* @param {Object} opts.languages the languages list
* @return {void}
*/
function setup({ languages = [], defaultLanguage = DEFAULT_LANGUAGE } = {}) {
if (!languages || !languages.length) {
throw new Error('opts.languages is mandatory');
}
/**
* Middleware
* @param {Object} req Express request
* @param {Object} res Express response
* @param {Function} next Express next handler
* @returns {void}
*/
return function middleware(req, res, next) {
const acceptLanguage = req.get('Accept-Language');
if (!acceptLanguage) {
req.language = defaultLanguage;
return next();
}
// parse and order the locales by priority
const parsedLanguages = parser.parse(acceptLanguage);
// validate languages
const userAcceptLanguages = _.filter(parsedLanguages, language =>
languageCodeExists(language.code)
);
// intersect user accept languages with the known languages list
const language =
findLanguageMatch(languages, userAcceptLanguages) || defaultLanguage;
req.language = language;
return next();
};
}
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